# Physics 1251 HW 3 #12

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I don't really understand where to go with this problem.  It seemed similar (at least part A) to part c of problem 8, but using that process I did not get the correct answer.  I am assuming that since this wall is an insulating wall and not a conducting wall, that is where the difference is, but I am not sure and do not know what to do. Some help on this problem would be awesome.
asked Sep 15, 2014 in General

Original Question: A slab of insulating material has a uniform positive charge density ρ, as shown in the figure below. The slab is infinite in the y and z directions.

It is similar to Q8 but in this case, it has a volume and need to use the volume charge density. To find the E-field at x>d/2, one can use the Gaussian surface show below:

$$\Phi_E=E2A=\frac {q_{in}}{\epsilon_0}=\frac {\rho Ad}{\epsilon_0}$$

For x<d/2, use the Gaussian surface inside the slab:

$$\Phi_E=EA=\frac {q_{in}}{\epsilon_0}=\frac {\rho Ax}{\epsilon_0}$$

Note that at the center, the E-field is zero and therefore, only one side of the Gaussian surface has flux.

answered Sep 16, 2014 by (21,750 points)